The present invention relates to the technical field of catalytically active systems and/or to the technical field of catalysts/catalytically active components on carrier materials.
The present invention more particularly relates to a method of preparing a catalyst system comprising at least one catalytically active component, in particular to a method of preparing a supported catalyst.
The present invention further relates to a catalyst system obtainable on the basis of the method according to the present invention and/or to a catalyst system as such, said catalyst system comprising at least one catalytically active component on a catalyst carrier, in particular at least one catalytically active component fixed to a catalyst carrier.
The present invention further also relates to methods of using the catalyst system of the present invention in the manufacture of filters and filter materials. The present invention further relates to methods of using the catalyst system of the present invention as a sorption store for gases or liquids or as a catalyst/catalyst carrier and also the use thereof for chemical catalysis. The present invention further relates to methods of using the catalyst system of the present invention in the catalysis of chemical processes and reactions. The present invention further relates to methods of using the catalyst system of the present invention in or as gas sensors or in fuel cells and also for sorptive, specifically chemisorptive, applications. The present invention further also relates to methods of using the catalyst system of the present invention for gas cleaning/purification and also for the removal of noxiants. The present invention further relates to methods of using the catalyst system to provide/reprocess cleanroom atmospheres. The present invention further also relates to protective materials as such, said protective materials being obtained by using the catalyst system of the present invention and/or comprising the catalyst system of the present invention. The present invention further also relates to filters and filter materials obtained by using the catalyst system of the present invention and/or comprising the catalyst system of the present invention.
A catalyst is generally a material/substance capable of raising the rate of a chemical reaction by lowering the activation energy without itself being consumed in the reaction.
Catalysts have immense technical and commercial significance in the prior art, for example in important catalytic processes, such as the so-called contact process for production of sulfuric acid, the catalytic process for methanol production and also the so-called Haber-Bosch process for industrial production of ammonia, and also the so-called Ostwald process for large scale industrial production of nitric acid by oxidation of ammonia. Catalysts are further employed in the synthesis of fine/specialty chemicals, in the synthesis of natural products and also in the manufacture of active pharmaceutical ingredients. More particularly, catalysts are also employed in catalytic hydrogenations.
The need for specific and powerful catalysts for use in chemical catalysis is generally high in the prior art, in particular because precise employment of catalysts enables faster and/or more energy-efficient chemical reactions. Hence the use of catalysts in chemical reactions is of immense commercial significance for that reason as well: a catalytic stage is believed to play a part in the underlying production/supply chain of about 80% of all chemical articles of manufacture.
In addition, catalysts also play an outstanding part in the area of environmental protection, in particular with regard to an exhaust gas aftertreatment in industry, for example in the context of industrial electricity generation and also in the treatment of exhaust gases in the field of road (passenger) transport.
Catalysts are in principle employable in the form of homogeneous or heterogeneous catalysts meaning that in the case of homogeneous catalysts, i.e., catalysts employed in homogeneous catalysis, the reactants underlying the reaction to be catalyzed and the catalyst are present in the same phase, whereas in the case of heterogeneous catalysts, i.e., catalysts employed in heterogeneous catalysis, corresponding reactants on the one hand and the catalyst on the other are present in different phases, for example as a solid catalyst and as liquid or gaseous reactants.
The advantages associated with employing heterogeneous catalysts reside in principle in particular in an occasionally improved separation/isolation of the catalyst from the reaction mixture, entailing the in-principle possibility of recycling the employed catalyst and/or of working up deactivated/inactive catalysts. Especially industrial processes often have a heterogeneous catalyst present in the form of a solid material and/or as a so-called contact (catalyst), while the reactants are employed in the form of gases or liquids. The aforementioned industrially established processes for example are such processes where the catalyst is employed in the form of a solid material.
Heterogeneous catalysts and/or catalysts in solid form often utilize metals and/or metal-containing compounds, such as metal salts and/or metal oxides, as catalysts. Catalysts of this type are for example employable therein in substance or alternatively in a form where the catalyst and/or its underlying catalytically active component is present on a carrier system and/or bound/fixed thereto.
Catalyst systems of this type, where the catalytically active component is present on a carrier, are generally known as supported catalysts.
Employing supported catalysts generally has the in-principle advantage of making it possible to realize larger surface areas and/or contact areas with the reactants to be converted, which generally leads to increased effectiveness and/or the employment of reduced amounts of catalyst with an attendant cost advantage.
Moreover, the employment of supported systems and/or catalysts is in principle associated with the advantage that the underlying catalysts are better to remove/separate from the reaction medium and also, in general, better to recycle. Especially catalysts employed in substance are difficult and/or very lossfull (in terms of catalyst mass) to segregate after reaction/conversion of the reactants, which generally serves to depress the economics and makes recycling of the catalysts used difficult in principle.
Supported catalysts/catalyst systems in the prior art may in principle take the form of supported structures that are compact or alternatively porous. The employment of so-called compact catalysts is associated in particular with the disadvantage that an efficient enlargement of surface area cannot be realized and therefore that catalytic activity can only be provided at the relatively small geometric surface area. By contrast, porous solids employed as catalyst carriers have enlarged surface areas which, as noted above, entails an increased effectiveness and/or a higher catalytic activity for a lower loading of catalyst.
Catalyst carriers employed include, for example, crystalline porous solids from the family of the zeolites, in particular in the field of petrochemistry and/or refinery technology to process/refine petroleum/crude oil. Pore sizes/diameters of zeolites are generally uniform, which provides a certain selective degree of reaction control through size alignment with the substances to be reacted. It is further in principle known in the prior art to employ silica, molecular sieves, metal oxides, such as aluminas, or alternatively ceramics as well as activated carbons as carrier systems for catalysts.
Carrier systems of this type are in principle also employed in order to enable a durable and/or elution-resistant fixing of specifically cost-intensive catalysts to reduce the respective losses during use and/or enable a corresponding recyclability, as noted above, and/or recovery of the catalyst system overall.
As far as the employment of activated carbon as a carrier material for catalysts specifically to obtain so-called activated carbon supported catalysts, in particular activated carbon supported noble metal catalysts, is concerned, the prior art generally employs activated carbons in the form of finely divided and/or pulverulent activated carbon (powdered carbon) and/or in the form of a finely ground powder, the corresponding particle sizes being in the lower μm range. Finely divided activated carbon is generally employed as a carrier system as an attempt to reduce limitations in the underlying mass transfer involved in the corresponding catalyzed target reaction, in particular through shortened diffusion/penetration paths into the porous structure of the activated carbon based carrier material. However, the employment of finely divided and/or pulverulent activated carbon as a catalyst carrier in the form of comparatively small particle sizes is associated with the central disadvantage that overall it is impossible to achieve optimum performance characteristics. For instance, the employment of finely divided activated carbon specifically in batch applications is caused by the low porosity in the filter cake bed and/or the high density of the bed formed from the underlying material to lead to inferior properties with regard to the segregation/separation of the catalyst/catalyst system after its use, in which connection it must be emphasized that the step of separating/filtering off the catalyst/catalyst system is an obligatory and/or absolutely required element of any catalytic batch process.
In-service conditions particularly of continuous catalytic processes employing pulverulent/finely divided activated carbon and/or powdered carbon in the reaction space are observed to result in an occasionally excessive densification of the catalyst system and hence in a high level of pressure drop and hence a reduced rate at which the reaction mixture comprising the corresponding reactants flows over the catalyst system. An excessive densification can also result when, as is often the case, the catalysts employed and/or the corresponding carrier materials lack abrasion hardness, and entails undesirable changes in the flow rate.
The performance characteristics of activated carbon supported catalyst systems are often also less than optimal in that the finely divided catalyst system is prone, particularly in a liquid medium comprising the reactants, to sludging and/or excessive densification, entailing a risk of plugging the reaction apparatuses and/or of excessively reducing the flow/filtration rate, adversely affecting catalytic conversion overall. Excessive densification of the catalyst system here may to a certain extent also result in “dead spaces” in the underlying apparatus, which result in a significantly reduced conversion of the reactants, which is similarly disadvantageous.
In general, the formation of sludged regions in the catalyst system is problematic/relevant in batch use in particular. Continuous catalytic applications where the underlying catalyst systems are for example introduced into corresponding reaction spaces, for example based on cartridge systems, and where a specifically continuous flow therethrough of a medium comprising the reactants takes place similarly give rise to the abovementioned high pressure drops with the corresponding lower flow rates for the catalyst system with the attendant disadvantages. Furthermore, to prevent the catalyst being dragged/flushed out by the continuous flow through the reaction system, there is often a need for costly filtration/retention devices which are prone to plugging.
It must accordingly be noted in summary that catalyst systems based on powderily/finely divided activated carbon as carrier material altogether do not always have adequate/satisfactory properties in respect of their application.
In order to reduce the disadvantages entailed by a small particle size, prior artisans have attempted to employ catalyst carriers based on particulate activated carbon while in principle contemplating in this regard starting materials for the activated carbon which are based on coconut shells, charcoal, wood (e.g., wood waste, peat, bituminous coal or the like). The activated carbons of the aforementioned type which result and/or are employed as catalyst carriers and may generally be in splint and/or granular form do in principle lead to a certain improvement in the performance characteristics, particularly with regard to the separation time in batch application, because this can be reduced on the basis of activated carbons, yet such activated carbons employed as catalyst carriers often have an insufficient level of mechanical stability, entailing an excessive attrition of the carrier material under in-service conditions, for example due to occasionally intensive agitation during the catalytic conversion. The low level of abrasion resistance on the part of such activated carbons then in turn leads via the corresponding comminution/grinding processes to finely divided particles entailing a high loss of catalytically active substance and the aforementioned disadvantages with regard to system sludgification/densification or the like.
In addition, the prior art concepts known for providing catalyst systems based on activated carbon as a carrier material are also disadvantageous because they often fail to enable optimal loading/fixing of the catalyst on the carrier material resulting not only in low amounts of catalyst being applied to the carrier but also in the frequent observation under in-service conditions of some release/leaching (elution) of the catalyst out of the carrier material, the leached amounts of catalyst being lost as a result, which is disadvantageous for technical as well as cost reasons. More particularly, the activated carbons which are employed in the prior art, in particular those which are based on coconut shells, often display a but low level of affinity for the catalyst to be applied/fixed and this—without wishing to be tied to this theory—is also caused by the underlying activated carbons often being hydrophobic at their pore surface and/or often not having an adequate amount of specifically polar functional groups to bind the catalyst (as is the case particularly with polymer based activated carbons, in particular PBSACs). However, this is detrimental to the loading properties as a whole, including specifically with regard to any durable fixing of the catalyst on the carrier system. The high loss of catalyst in relation to the underlying catalyst system similarly entails a reduction in the reactant conversion of the underlying catalytic reactions, which also serves to depress the economics of the catalyst systems employed.
Since conventional activated carbon is apolar and/or hydrophobic at its surface and therefore does not display any significant affinity for catalytically active components/catalysts to be applied/fixed which are employed for reactive/catalytic endowment of the activated carbon, the preparation/endowment of the activated carbon with the catalyst requires the employment of a large excess of catalyst substance in order to ensure any loading of the activated carbon at all. More particularly, the catalysts generally only adhere via purely physical interactions and may therefore also be removed again in part at least particularly on contact with liquids (e.g., as in elution processes or the like).
DE 29 36 362 C2 describes a method of preparing a palladium-carbon catalyst wherein reduction is used to deposit palladium on a carbon catalyst carrier suspended in an organic solvent. Palladium is stated in this context to be deposited as metal on the suspended carrier. The carbon carrier used is pulverulent activated carbon, carbon black or graphite. However, the catalysts described do occasionally entail the disadvantages described above, particularly regarding the segregation/recovery of the catalyst particularly in batch type catalytic processes as well as its performance characteristics in continuous catalytic processes, particularly with regard to pressure drop and/or flow rate.
It must thus be stated in summary that the prior art catalyst systems based on conventional activated carbons and/or pulverulent activated carbons as employed carrier material have both manufacturing—but also use-specific disadvantages, in particular with regard to the loading with a catalytically active component and also its fixing on the material on the one hand but also with regard to the use of the underlying systems in continuous and also batch type applications in catalysis.